1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming apparatus having a punch apparatus that punches a hole in a sheet.
2. Description of the Related Art
Conventionally, some sheet processing apparatuses have a punch apparatus that punches a hole in a sheet one by one while the sheet is conveyed after images are formed on them. Japanese Patent Laid-Open No. 2007-055748 discusses the invention about such a sheet processing apparatus.
The sheet processing apparatus discussed in Japanese Patent Laid-Open No. 2007-055748 includes a lateral registration correcting portion that moves a sheet in a width direction orthogonal to a sheet conveying direction to align with a punch position. More specifically, the sheet processing apparatus discussed in Japanese Patent Laid-Open No. 2007-055748 includes first and second lateral registration correcting portions. The first lateral registration correcting portion corrects the lateral registration based on a lateral registration detection result at the downstream end in the sheet conveying direction. The second lateral registration correcting portion corrects the lateral registration based on a lateral registration detection result at the upstream end in the sheet conveying direction. This configuration prevents lateral registration due to skew feeding of the sheet and highly accurately punches a hole in the sheet.
However, the sheet processing apparatus discussed in Japanese Patent Laid-Open No. 2007-055748 corrects the second lateral registration by switching back a sheet to correct the skew feeding. It takes time from the beginning to the end of the lateral registration correction. As a result, the time to punch a hole in a sheet might become long.
The present invention provides a sheet processing apparatus that can correct skew feeding of sheet and shorten the time to punch a hole in a sheet.